Metal oxide particles have long been used to make catalysts, and particularly catalyst supports. The useful metal oxides include alumina, silica, titania, zirconia, spinel, and mixtures thereof. One particularly useful metal oxide is gamma-alumina, especially gamma-alumina derived from boehmite or a boehmitic gel.
One of the problems encountered with high surface area metal oxide catalyst supports is that they lose surface area upon being heated to high temperatures, especially when moisture is present. In order to improve surface area retention at high temperatures, prior art workers have mixed alumina with transition metal oxides and rare earth metal oxides such as lanthanam oxide, barium oxide and ceria. Two other useful additives are silica and phosphates. The prior art additives generally suffer from an inability to stabilize metal oxide surface area upon heating to high temperatures on the order of about 1000.degree. C., especially when the metal oxides are heated for several hours or more in the presence of moisture.
Silica and phosphate additions to alumina catalysts are known to retard surface area degradation upon heating. One problem with addition to alumina of high levels of silica and phosphate is interference with catalyst activity in finished catalysts made with the stabilized alumina.
Lachman et al U.S. Pat. Nos. 5,039,644 and 5,124,302 disclose monolithic catalyst supports made with porous metal oxide material stabilized by phosphate dispersed substantially throughout the metal oxide. The phosphate is said to stabilize the porous metal oxide material against thermal degradation during sintering or other exposure to elevated temperatures, thereby aiding retention of higher overall surface area. The present invention improves upon the methods and products disclosed by Lachman et al.
A principal objective of the present invention is to provide a method for making catalyst particles having improved resistance to loss of surface area by thermal degradation.
A related objective is to provide an improved catalyst product made by the method of the present invention.
Additional objectives and advantages of our invention will become apparent to persons skilled in the art from the following detailed description.